Atrial fibrillation surgery involving radiofrequency, D.C., microwave, or other thermal ablation of atrial tissue has a limitation in that tissue contact throughout the length of the electrode(s) is/are not consistent causing variability in the transmission of energy throughout the target length of ablated/coagulated tissue. This produces gaps of viable tissue that promote propagation of wavelets that sustain atrial fibrillation, or produce atrial flutter, atrial tachycardia, or other arrhythmia substrate.
Another influence in the inability of existing thermal ablation probes to create complete curvilinear, transmural lesions is the presence of convective cooling on the opposite surface of the atrium producing a heat sink that decreases the maximum temperature at this surface thereby preventing the lesions from consistently extending transmurally through the entire wall of the atrium. This is especially relevant during beating-heart procedures in which the coagulation/ablation probe is placed against the epicardial surface, and blood flowing along the endocardium removes heat thus producing a larger gradient between temperature immediately under the probe electrodes along the epicardium and that at the endocardium.
Another deficiency of current approaches is the inability to direct the coagulation of precise regions of soft tissue while avoiding underlying or nearby tissue structures. For example, atrial fibrillation ablation may involve extending a lesion to the annulus near which the circumflex, right coronary artery, and coronary sinus reside; another example involves ablating ventricular tachycardia substrates that reside near coronary arteries or coronary veins. Conventional approaches are unable to selectively ablate desired soft tissue structures and isolate preserved tissue structures from targeted regions.
Aspects of the invention address at least some of these deficiencies for atrial fibrillation and ventricular tachycardia ablation. In addition, die variations of the invention address similar deficiencies, which are apparent during other applications involving coagulation of a selected tissue region in a precise manner such as cancer ablation, soft tissue shrinking, and articular cartilage removal.